Communication channels in telecommunication systems can often be measured with a sufficiently good accuracy in a receiver unit but often not in the transmitter unit. However, transmitter units in communication systems can benefit from knowing the properties of said channels through adapting the transmitted signal, e.g., power, frequency, modulation scheme, or coding to said channel properties. It is therefore desirable to report results of channel measurements from a receiver unit, which can perform such measurements with the necessary accuracy, to the transmitter unit, which needs indications of such measurements for adaptation of the transmitted signal.
In a prior art solution, which is used in present communications systems, e.g. GSM-systems or WCDMA-systems, mobile terminals can be instructed to periodically report the downlink channel quality to the transmission unit in the network. This can be used for, e.g., Transmit Power Command (TPC-) messages, which are derived inter alia from the receiver's perception of the downlink channel, and transmitted back to the transmitter unit as an incremental value to increase or decrease the downlink transmission power. This is described, e.g., in the technical specification TS25.214 (V.5.0.0) issued by the 3rd Generation Partnership Project (3GPP). A low-detail knowledge of the channel, e.g. as a representation of the channel quality, can be useful to adapt the bit rate, and coding and modulation formats in the transmitter. However, such simple channel quality reporting provides a too low level of detail for advanced adaptation of the transmitted signal, e.g. allocation of and power control for sub-carriers in an OFDM system, and is thus not useful for systems employing such techniques.